Gonadotropin-releasing hormone is a peptide of 10 amino acids and is also known as luteinizing-hormone releasing hormone (LHRH). Gonadotropin-releasing hormone is produced in the hypothalamus, and is responsible for the release of follicle-stimulating hormone and luteinizing hormone from the pituitary gland. Gonadotropin-releasing hormone is released from neurons in the hypothalamus, and plays a role in the complex regulation of follicle-stimulating hormone and luteinizing hormone release. Follicle-stimulating hormone and luteinizing hormone, in combination, regulate the functioning of the gonads to produce testosterone in the testes and progesterone and estrogen in the ovaries, and regulate the production and maturation of gametes. For example, follicle-stimulating hormone stimulates the growth and recruitment of immature ovarian follicles in the ovary, and luteinizing hormone triggers ovulation.
There are differences in gonadotropin-releasing hormone secretion between females and males. In males, gonadotropin-releasing hormone is secreted in pulses at a constant frequency, but in females the frequency of the pulses varies during the estrus cycle and there is a large surge of gonadotropin-releasing hormone just before ovulation. Gonadotropin-releasing hormone secretion is pulsatile in all vertebrates, and is necessary for correct reproductive function. Thus, gonadotropin-releasing hormone controls a complex process of follicular growth, ovulation, and corpus luteum maintenance in the female, and spermatogenesis in the male.
Gonadotropin-releasing hormone has been isolated and characterized as a decapeptide. Synthetic forms of gonadotropin-releasing hormone are available and modifications of the decapeptide structure of gonadotropin-releasing hormone have led to multiple gonadotropin-releasing hormone analogs that either stimulate (e.g., gonadotropin-releasing hormone agonists) or suppress (e.g., gonadotropin-releasing hormone antagonists) the release of the gonadotropins, such as luteinizing hormone and follicle-stimulating hormone.
It is important to commercial swine production to maximize reproductive efficiency to make swine production more profitable. There has been heavy reliance on daily heat detection of individual female swine with the associated labor costs devoted to manual detection of heat in the female swine based on daily checks of gilts or sows to achieve the best results with, for example, artificial insemination. Heat detection using labor intensive methods, such as daily checks, increases the probability of success with artificial insemination. Thus, devoting time, manual labor, and materials costs to daily checks for heat detection is necessary because it is difficult to predict the time of heat (i.e., the best time for insemination) without using methods requiring a daily regimen for monitoring heat detection. Accordingly, methods are needed to optimize the success of insemination of animals, without heat detection, to reduce the labor costs, and to increase the profitability of swine production.